1. Field of the Invention
The present disclosure relates to blades, and more particularly to blade tip surfaces such as those for cooperating with abradable coatings on turbomachines, such as in gas turbine engines.
2. Description of Related Art
A variety of rotating blades are known for use in gas turbine engines. Traditionally, air seals are used between rotating blades and the inner surface of the engine case in order to increase engine efficiency. Engine efficiency can be correlated to the clearance between tips of the blades and the inner diameter of the air seal. In this regard, some air seals are provided as an abradable air seal that incorporates an abradable material affixed to the inner surface of a casing. During operation, the rotating blade tips of the blades contact and abrade the abradable material (also known as “rubbing”).
Performance requirements for abradable air seal systems can include efficiency standards and maintenance cost targets, among other requirements. In order to meet these standards, abradable air seal systems can be required to have low gas permeability, low roughness, good erosion resistance, but still be abradable during interaction with blades. These requirements can conflict with one another, for example, typically the more erosion resistant an air seal is, the greater the increase in the density and hardness of the seal, tending to increase the difficulty of abrading such a seal. In order to cut the hard and dense abradable material, blades can include abrasive tip coatings such as Cubic Boron Nitride (CBN), which tends to increase the cost of the blades.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved blades for use in sealing systems. The present disclosure provides solutions for these problems.